Natural gas has become increasingly attractive as an energy source for operating engines. Natural gas as a fuel has the advantages of wide flammability limits, improved fuel economy and lower NO.sub.x emissions. With the usual gas engines, lowering of the NO.sub.x in the exhaust results in the presence of higher quantities of unburned hydrocarbons in the exhaust.
U.S. Pat. No. 1,422,794 issued to F. A. Smith on Jul. 11, 1922 illustrates an ignition device for internal combustion engines that incorporates two or more precombustion chambers somewhat similar to those proposed hereinafter. The upper chambers are provided with a spark plug and a rich fuel is supplied thereinto to assure that ignition of the fuel occurs. The flame initiated in the upper chamber is discharged into the lower chamber and subsequently into the combustion chamber of the engine to ignite the main fuel charge. The device is air cooled and is intended for use with gasoline as fuel.
U.S. Pat. No. 3,066,662 issued to C. H. May, et al. on Dec. 4, 1962 illustrates an ignition device that is very similar to that as described in the Smith patent. The purpose of the May, et al. patent is also to promote the combustion of a lean fuel in the main combustion chamber by igniting a relatively rich fuel in one of the precombustion chambers of the engine. In the precombustion chamber arrangement illustrated, two convergent/divergent nozzles are provided which together comprise a relatively long and bulky device that is located externally of the engine and, therefore, is air cooled as was the ignition device disclosed in the Smith patent.
An object of this invention is to provide an improved ignition device for spark-ignited, gas engines that can be located within the head of the engine within the confines of the water jacket for cooling purposes and that comprises a pair of precombustion chambers of generally cylindrical configuration that are separated by an orifice and have an orifice of larger size connecting the second precombustion chamber with the combustion chamber of the engine.